Device for distinguishing atrial from ventricular depolarisations

Abstract: The invention relates to a method for determining whether electrical signals in a heart are caused by atrial depolarizations or ventricular depolarizations. When heart signals are sensed in the upper part of the ventricular heart tissue, preferably the upper part of the ventricular septum (10), the detection of heart signals from both the atrium and ventricle and identification of depolarization is facilitated if the course of the signals is sensed, whereby monophasic heart signals are caused by an atrial depolarization and biphasic signals are caused by a ventricular depolarization.

Description: The invention relates to a device for sensing electrical signals in the ventricular heart tissue and distinguishing sensed electrical signals caused by atrial depolarizations from sensed electrical signals caused by ventricular depolarizations. In a healthy heart, a heart beat commences with a spontaneously generated electrical impulse in the sinus node. The impulse first induces atrial depolarization resulting in contraction of atrial heart muscle (atrial systole). The contraction of atrial musculature pumps blood from the respective atrium down to the ventricles. After a delay, the impulse is then conducted to the ventricles via the A-V node and causes ventricular depolarization, resulting in a contraction of ventricular heart muscle (ventricular systole). The contraction of ventricular muscle expels blood out of the heart into the systemic circulation and the pulmonary circulation. Heart tissue in the atrium and ventricle then repolarizes in turn, and the muscle tissue relaxes (diastole). The heart then refills with blood from the veins. As the sinus node generates a new impulse, the cycle restarts. For people with certain heart defects, a pacemaker can be an excellent aid which is capable of taking over stimulation of heart tissue when natural, spontaneous self-stimulation is inoperative. When e.g. the A-V node blocks transmission of signals from the atria but the sinus node works properly, triggering atrial depolarization in a natural way, a pacemaker capable of stimulating ventricular heart tissue, so the stimulated heart cycle resembles a healthy heart's cardiac cycle as closely as possible, would be advantageous. In order to acieve this, it must be possible to detect atrial depolarizations at the same time as it must be possible to deliver stimulation pulses to the ventricular tissue. Here, the use of dual chamber pacemakers, in which a first electrode with an electrode surface is placed in the right atrium to sense atrial depolarizations and a second electrode with an electrode surface is placed in the apex of the right ventricle to stimulate the ventricular tissue, is known. One such pacemaker is described in US-A-4,343,311. At least two electrodes must be introduced into the heart, making the system more complex. Complications can develop during the implantation of the electrodes, and there is an increased risk of faults. In addition, a plurality of electrodes impedes the return of blood to the heart to some extent. In order to reduce the number of electrodes which must be introduced into the heart via the venous system, a multipolar electrode can be devised so it has at least one electrode surface in the ventricle to stimulate same and at least one electrode surface in the atrium to sense atrial depolarizations. One such electrode is described in US-A-4,444,195. For reliable detection of atrial depolarizations, the electrode surface in the atrium should be in close proximity to atrial tissue. The electrode must therefore be so stiff that it remains in virtually constant contact with atrial tissue. This could irritate heart tissue during the muscular contractions. In general, a multipolar electrode also has a larger diameter than a unipolar electrode. Both when a plurality of electrodes, each with one electrode conductor, is used and when multipolar electrodes, with a plurality of electrode conductors, is used, conductor breakage is always a risk. The more conductors employed, the greater the likelihood that one of them has a slight defect or reduced abrasion resistance, despite careful fabrication and quality control. In US-A-4,905,696 a detector is described which unipolarly measures heart impedance in the ventricle, and from the impedance signal atrial depolarizations can be identified as fast, brief changes. In the closest prior art document, EP-A-0600200, which falls under Art. 54C3) EPC, a detector is described which comprises at least two integrators. The heart's electrical signals are sensed. Monophasic and biphasic signals can be distinguished when the respective integrator integrates signals with different polarity. Since depolarizations in the atrium are monophasic when the signal is sensed in the ventricle and ventricular depolarizations are biphasic when sensed in the ventricle, this detector can distinguish between depolarization in the atrium and ventricle respectively on the basis of electrical signals detected unipolarly in the ventricle. However, the aforementioned patent application, like the other prior art described, does not consider the way the signals should be picked up so the most reliable discrimination possible is achieved. Nor do they address the issue of how to reduce the irritation to which heart tissue is subjected. One object of the invention is to achieve a device for performing a method for distinguishing the atrial depolarizations from the ventricular depolarizations, when electrical signals are sensed in the ventricle, in the safest and most effective way possible. The method will simultaneously permit the most natural possible stimulation of the ventricle, and the electrode implanted in the heart will impede heart movements as little as possible. In accordance with the invention the electrode lead is designed so that the first electrode surface may be positioned in such a way that it senses the electrical signals in the part of the ventricular tissue located nearest the atrial half of the heart. Sensing of electrical signals in the upper part of the ventricle's heart tissue will make it easier to detect signals from both the atrium and ventricle. Here, different types of detectors can be used for discriminating signals. A few are described in conjunction with the description of a device for performing the method. To sense electrical signals in the upper part of the ventricle, the electrode is introduced into the heart in such a way that it assumes a gentle bend in the ventricle, and the electrode surface is positioned so it becomes embedded in heart tissue. The electrode's gentle bend will reduce the irritation caused by the electrode conductor during the heart's contraction phase. This is because the heart pulls the septum between the atrium and ventricle (the valve plane), at which outlets into the blood circulations are located, down towards the apex during each ventricular contraction. The gentle bend resiliently distributes the electrode's surface over a larger part of the heart tissue. So mechanical pressure exerted by the electrode at contraction movements is therefore reduced. The risk of inflammation etc. in tissue accordingly declines. The mechanical load on the electrode and the risk of fatigue failure also decline simultaneously. In connection with this, it is advantageous if the first electrode is positioned so it senses electrical signals in the ventricular septum. Since the depolarization wave in a healthy heart is conducted to the ventricle via the A-V node, which is sited in the upper part of the ventricular septum, this electrode position will simplify the sensing and identification of atrial signals, since the electrode surface will be closer to atrial musculature. Moreover, this position will produce the most natural depolarization effect possible when the ventricle is stimulated. As previously noted, atrial depolarizations are experienced as being monophasic when sensed in the ventricle, and ventricular depolarizations are experienced as biphasic. It is therefore an advantage if atrial depolarizations are distinguished from ventricular depolarizations by determining whether the sensed electrical signals have a monophasic or biphasic course, whereby monophasic courses are interpreted as atrial depolarizations and biphasic courses are interpreted as ventricular depolarizations. In addition, the biphasic aspect of the signal for the ventricular depolarization will be more pronounced when measurement occurs high up in the ventricle, compared to measurement in the apex. A detector capable of doing this is, as noted above, the subject of an earlier filed patent application. Other detectors will be described below in the present application. To increase reliability in the identification of atrial depolarization, it is advantageous if the duration of the monophasic courses is determined and only monophasic courses with a duration less than a predetermined duration are interpreted as atrial depolarizations. This means that since even ventricular repolarizations, which also have a monophasic course, are sensed, these can easily be distinguished from the atrial depolarizations, since the former has a much longer duration. A device according to the invention for determining whether electrical signals in a heart are caused by an atrial depolarization or a ventricular depolarization, comprises an electrode lead with a first electrode surface, a detector for sensing electrical signals via the first electrode surface and a control device for distinguishing atrial depolarizations from ventricular depolarizations on the basis of the electrical signals sensed by the detector. The electrode lead is designed to be introduced into the right ventricle and positioned with a gentle bend so the first electrode surface is attachable to the upper part of the ventricular septum. The detector comprises means for distinguishing between signals caused by atrial depolarizations and signals caused by ventricular depolarizations. The means for distinguishing between signals caused by atrial depolarizations and signals caused by ventricular depolarizations comprises a low-pass filter for eliminating high-frequency noise, a first comparator, which compares the amplitude of the filtered signal with a first threshold value and emits an output signal when the filtered signal's amplitude exceeds the first threshold value, and a second comparator, which compares the amplitude of the filtered signal with a negative second threshold value and emits an output signal when the filtered signal's amplitude is less than the second threshold value, whereby the control device interprets signals generating an output signal only from the first comparator as an atrial depolarization and signals generating an output signal from both comparators as a ventricular depolarization. Since the signals can be discriminated because atrial depolarizations are monophasic, whereas ventricular depolarizations are biphasic, identification of the respective signal with a detector, in which the signal's amplitude is compared with a threshold value on either side of a baseline level, is simple. Monophasic signals can only satisfy the condition for one threshold value, whereas a biphasic signal can satisfy conditions for both threshold values. In this context, it is advantageous if the control device comprises a timer for measuring the time during which the first comparator emits an output signal, whereby sensed heart signals which generates an output signal from the first comparator with a duration less than a predetermined duration is interpreted as an atrial depolarization. This would prevent spurious interpretation of ventricular repolarization as atrial depolarization. It is advantageous if the device comprises a pulse generator for generating and emitting stimulation pulses to the ventricular tissue via the first electrode surface and that the control device controls the pulse generator on the basis of the electrical signals sensed by the detector. Referring to four figures, the invention will be described in greater detail below, whereby FIG. 1 shows an embodiment of a unipolar pacemaker; FIG. 2 illustrates the electrical signal picked up from a heart; FIG. 3 shows in a block diagram the structure of the unipolar pacemaker in greater detail; FIG. 4 illustrates an embodiment of a detector which can separate monophasic signals from biphasic signals; FIG. 5 illustrates the output signals from the detector according to the first embodiment; FIG. 6 shows an embodiment of a bipolar pacemaker, and FIG. 7 shows in a block diagram the structure of the bipolar pacemaker in greater detail. A unipolar pacemaker 2, as shown in FIG. 1, is connected to a heart 4 by an electrode lead 6. At the end of the electrode lead 6 there is a tip electrode 8, which is attached to the upper part of the ventricular septum 10 in the right ventricle of the heart 4. The electrode lead 6 has an electrode conductor 12, which connects the tip electrode 8 to pacemaker electronics. On the pacemaker 2 is an indifferent electrode 14 placed so a stimulation pulse can be delivered to the heart 4 from the pacemaker 2 via the electrode lead 6 and the tip electrode 8 to the septum 10. The stimulation pulse is then conducted back through body tissue to the indifferent electrode 14. The electrical signals of the heart can also be sensed via the tip electrode 8. The gentle bend in the electrode lead 6 in the ventricle and the position of the tip electrode 8 high up in the septum 10 cause less irritation to heart tissue than if the tip electrode 8 were located in the apex. Since the heart muscle's contraction pulls the valve plane down towards the apex in order to pump blood out intc the respective blood circulations, the surface of the electrode lead 6 is distributed over a larger part of heart tissue, and the lead resiliently follows changes in the shape of the ventricle. The gentle bend and the position high up in the septum 10 do not impede the heart's natural movements, and the load on the electrode conductor 12 is also reduced. Heart signals 15 are sensed through the tip electrode 8, as shown in FIG. 2. Heart signals can be subdivided into three groups, first the atrial depolarization, i.e. the P wave, followed by the ventricular depolarization, i.e. the QRS wave, and the ventricular repolarization, i.e. the T wave. The atrium is also repolarized, but the signal from this repolarization is generally "swamped" by the QRS wave. As the signal 15 shows, the P wave and the T wave are monophasic, whereas the QRS wave is biphasic. This is utilized in the unipolar pacemaker 2 to reliably distinguish between atrial depolarization and ventricular depolarization. In FIG. 3 is shown the unipolar pacemaker 2 in a block diagram. A pulse generator 16 generates stimulation pulses and deliver same, via the electrode conductor 12, to the tip electrode 8. The pulse generator 16 is also connected to the indifferent electrode 14. The pulse generator's 16 emission of stimulation pulses and the amplitude and duration of the stimulation pulses are controlled by a control device 18. A detector 20 is connected in parallel across the pulse generator's 16 output terminal in order to sense heart signals. The position of the electrode tip 8 high up on the septum 10 (FIG. 1) simplifies detection by the detector 20 of signals from both the atrium and the ventricle. The detector's 20 sensing of heart signals and determination of the threshold level for detectable signals are controlled by the control device 18. The pacemaker 2 also comprises a telemetry unit 28 which is connected to the control device 18. Via the telemetry unit 28, information can be transmitted to/from the control device 18 from/to an extracorporeal programming unit. An embodiment of the detector 20 is shown in FIG. 4. The tip electrode 8 is connected by the electrode conductor 12 to a capacitor 21 which eliminates DC components and maintains a given baseline level for the signal. The sensed signals are then fed through a low-pass filter 22, suitably with a limit frequency of 100 Hz, to reduce noise from muscle signals and other noise. The filtered signal then goes to a first comparator 23 and a second comparator 24. The filtered signal is compared with a positive threshold value V POS in the first comparator 23, and the filtered signal is compared with a - negative threshold value V NEG in the second comparator. The two thresholds can have the same or different absolute values. The first comparator 23 and the second comparator 24 generate an output signal as long as the filtered signal is greater than the first threshold value or is less than the second threshold value respectively. Output signals from the comparators 23, 24 are sent to the control device 18. In FIG. 5 is illustrated the output signals from the respective comparator 23, 24 for the input signal 15 to the detector 20 as shown in FIG. 2. The signal 25 shows the output signal from the first comparator 23, and the signal 26 shows the output signal from the second comparator 24. The P wave from the signal 15 in FIG. 2 will generate a square wave 27 from the first comparator 23, the QRS wave will generate a brief square wave 29 from the first comparator 23 and a brief square wave 31 from the second comparator 24 and the T wave will generate a long-duration square wave 33 from the first comparator 23. Since the second comparator 24 only generates an output signal when a biphasic signal is present, ventricular depolarizations are very easy to identify. Since the T wave generates a long square wave 33, the control device 18 can appropriately be devised so only output signals from the first comparator 23 which are less than a predetermined duration are interpreted as atrial depolarization. In FIG. 6 is shown a bipolar pacemaker 132 connected to a heart 134 via an electrode lead 136. The electrode lead 136 has been introduced into the right ventricle and anchored with a tip electrode 138 in the upper part of the ventricular septum 140. The electrode lead 136 has been introduced into the ventricle with a gentle bend contributing to a reduction in irritation of heart tissue around the tip electrode 138. A ring electrode 142 is located at a predetermined distance from the tip electrode 138 and presses against the septum 140. The tip electrode 138 is connected to pace electronics via a first electrode conductor 144, and the ring electrode 142 is connected to pace electronics via a second electrode conductor 146. The pacemaker 132 also comprises an indifferent electrode 148 which is also connected to pace electronics. Stimulation pulses can be delivered to ventricular tissue either unipolarly via the first electrode conductor 144, the tip electrode 138, heart tissue and the indifferent electrode 148, or bipolarly via the first electrode conductor 144, the tip electrode 138, heart tissue, the ring electrode 142 and the second electrode conductor 146. The ring electrode 142 then functions as an indifferent electrode. Both the tip electrode 138 and the ring electrode 142 can sense the heart's 134 electrical activity. The pacemaker 132 is shown in a block diagram in FIG. 7 and has a stimulation pulse generator 150 connected to the first electrode conductor 144 and to the second electrode conductor 146. The pulse generator 150 is also connected to the indifferent electrode 148. A control device 152 controls the pulse generator's emission of stimulation pulses and pulse amplitude and duration. The control device 152 also decides whether the pulse generator 150 is to emit unipolar or bipolar stimulation pulses. A detector unit 154 (which is not claimed according to the invention) is connected in parallel across the pulse generator's 150 output terminal. Here, the detector unit 154 comprises a first detector 156, connected across the first electrode conductor 144 and the indifferent electrode 148, to detect heart signals at the tip electrode 138 and a second detector 158, connected to the second electrode conductor 146 and the indifferent electrode 148, to sense heart signals at the ring electrode 142. Sensed signals are sent to the control device 152 which, in turn, can control the detector unit 154, e.g. when the detectors 156, 158 are to sense heart signals and the sensitivity with which the heart signals are to be sensed. Like the unipolar pacemaker 2 in FIG. 3, the bipolar pacemaker 132 comprises a telemetry unit 160 through which information can be transmitted to/from the control device 152 from/to a programming unit 162. When atrial depolarization occurs, the atrial heart signal is sensed by the tip electrode 138 and therefore interpreted as atrial depolarization. In the upper part of the ventricular septum 140, ventricular depolarization has a propagation direction from the bottom up, i.e. it is first sensed by the ring electrode 142 and then by the tip electrode 138. The control device 152 can therefore easily distinguish between atrial depolarization, only sensed by the tip electrode 138, and ventricular depolarization, sensed both by the ring electrode 142 and the tip electrode 138. In those instances in which the detectors 156, 158 are not equipped with filters which eliminates the T wave, this wave can also be easily identified. This is because ventricular repolarization has a more stochastic course of propagation than the depolarization and can therefore e.g. be sensed simultaneously by the tip electrode 138 and the ring electrode 142 or even first by the tip electrode 138 and then by the ring electrode 142. Repolarization can also be identified in the corresponding way as with the unipolar pacemaker 2. Ventricular repolarization have a relatively constant amplitude when it follows spontaneous depolarization. Since the control device 152 also senses the amplitude of heart signals, the repolarization signal can be easily identified. This circumstance can also be utilized for distinguishing between spontaneous and stimulated ventricular depolarizations. If ventricular repolarization is identified, identification of depolarization becomes possible, since ventricular repolarization cannot follow atrial depolarization without an intervening ventricular depolarization. Like the unipolar pacemaker 2, the bipolar pacemaker 132 can even be devised to sense whether heart signals are monophasic or biphasic and measure the interval between various depolarizations and repolarizations. If heart signals are sensed as to whether they are monophasic or biphasic at the tip electrode 138, the bipolar pacemaker 132 can operate solely in a unipolar mode, i.e. if the second electrode conductor 146 broke, the pacemaker 138 would operate in the same way as the unipolar pacemaker 2. A plurality of the described functions can be used in the corresponding manner with both unipolar and bipolar electrodes.

Claims: A device (2; 132) for determining whether electrical signals in a heart (4; 134) are caused by an atrial depolarization or a ventricular depolarization, comprising an indifferent electrode (14; 148), an electrode lead (6; 136) with a first electrode surface (8, 138), the electrode lead (6; 136) being designed to be introduced into the right ventricle and positioned with a gentle bend so the first electrode surface (8; 138) is attachable to the upper part of the ventricular septum (10; 140), a detector (20) for sensing electrical signals via the first electrode surface (8; 138) and a control device (18; 152) for distinguishing atrial depolarizations from ventricular depolarizations on the basis of electrical signals sensed by the detector (20), which comprises means (21-24) for distinguishing between signals caused by atrial depolarizations and signals caused by ventricular depolarizations, which means (21-24) comprises a low-pass filter (22) for eliminating high-frequency noise, a first comparator (23) which compares the amplitude of the filtered signal with a first treshold value (V POS ) and emits an output signal when the filtered signal's amplitude exceeds the threshold value (V POS ), and a second comparator (24), which compares the amplitude of the filtered signal with a negative second threshold value (V NEG ), and emits an output signal when the filtered signal's amplitude is less than the second threshold value (V NEG ), whereby the control device (18) interprets signals generating an output signal only from the first comparator (22) as an atrial depolarization and signals generating an output signal from both comparators (22, 23) as a ventricular depolarization. A device according to claim 1, characterized in that the control device (18) comprises a timer for measuring the time during which the first comparator (22) emits an output signal, whereby a sensed heart signal which generates an output signal from the first comparator (22) with a duration less than a predetermined duration is interpreted as an atrial depolarization.

Inventors: EKWALL CHRISTER, EKWALL, CHRISTER
Applicants: ST JUDE MEDICAL, ST. JUDE MEDICAL AB
Application year: 1994
Main classification: A61N1
IPC codes: A61N1, A61B5